When extracted, mineral oil is generally obtained as a relatively stable water-oil emulsion. According to the age and deposit, this may comprise up to 95% by weight of water. The water may firstly be water already present in the deposit, and secondly water which is injected into the deposit in the course of secondary and/or tertiary mineral oil extraction through injection boreholes. Generally even greater amounts of salts are dissolved in the water, for example alkali metal or alkaline earth metal salts, and the emulsion typically further also comprises solids which are discharged from the borehole with the oil-water emulsion. The water-oil emulsions are stabilized by natural emulsifiers which occur in the crude oil, for example naphthenic acids. They may also additionally be stabilized by emulsifiers which do not occur naturally, for example surfactants which have been introduced into the mineral oil deposit for tertiary mineral oil extraction and are now discharged again with the oil thus extracted.
Water, salts and solids have to be removed before the processing of the crude oil in the refinery. Refineries frequently require that the water content of the crude oil supplied must not be more than 1%. For economic reasons, the water and the further components are removed from the crude oil while still at the site of extraction in order to avoid the uneconomic transport of water and to prevent or at least to minimize corrosion problems.
The phase separation of the water-oil emulsion should be as rapid and as complete as possible. Only in this way, in view of the large conveying volumes, can the apparatus for phase separation, for example settling tanks, be kept at a minimum size. On extraction platforms at sea, the use of very small, compact apparatus for phase separation is a necessity in construction terms owing to the limited space, and small systems of course generally require lower capital costs than large systems. A requirement often made is that the phase separation should not take more than approx. 20 to 30 min.
It is known that emulsion splitters (demulsifiers) can be used to accelerate the phase separation of oil-water emulsions. Emulsion splitters are interface-active substances which influence the oil-water interfaces and thus contribute to more rapid phase separation. EP-A 0 264 841 describes the use of linear copolymers composed of hydrophobic acrylic esters or methacrylic esters and hydrophilic ethylenically unsaturated monomers as mineral oil emulsion splitters.
EP-A 0 499 068 describes the preparation of reaction products of vinylic monomers and alcohol alkoxylates or phenol alkoxylates and their use as demulsifiers for crude oil emulsions.
U.S. Pat. No. 5,460,750 describes reaction products of phenol resins and alkylene oxides as emulsion splitters for crude oil emulsions.
EP-A 0 541 018 describes emulsion splitters prepared from polyethyleneimines having a weight-average molecular weight of up to 35 000 g/mol and ethylene oxide and propylene oxide, and a second active component used additionally is an alkylphenol-formaldehyde resin.
EP-A 0 784 645 describes the preparation of alkoxylates of polyamines, especially of polyethyleneimines and polyvinylamines, and their use as crude oil emulsion splitters.
EP-A 0 267 517 discloses branched polyamino esters as demulsifiers. The branched polyamino esters are obtained by reacting alkoxylated primary amines with triols and dicarboxylic acids.
In addition, dendrimeric polymers have been described as demulsifiers for crude oil.
U.S. Pat. No. 4,507,466 and U.S. Pat. No. 4,857,599 disclose dendrimeric polyamido amines. U.S. Pat. No. 4,568,737 discloses dendrimeric polyamido amines and hybrid dendrimers formed from polyamido amines, polyesters and polyethers, and their use as demulsifiers for crude oil. The preparation of dendrimers is very costly and inconvenient (see below), and these products are therefore very expensive and hardly usable in an economically viable manner in industrial scale applications.
DE 103 29 723 describes the preparation of alkoxylated dendrimeric polyesters and their use as biodegradable emulsion splitters. The dendrimeric polyesters used are based on a polyfunctional alcohol as the core molecule and a carboxylic acid which has at least two hydroxyl groups as a structural component. Structural components which have both an acid function and at least two hydroxyl functions, known as AB2 units, are comparatively rare and therefore expensive. Moreover, the formation of dendrimers is inconvenient and costly (see below).
WO2006/084816 A1 discloses the use of nondendrimeric high-functionality hyperbranched polyesters which are obtainable by reacting at least one aliphatic, cycloaliphatic, araliphatic or aromatic dicarboxylic acid (A2) or derivatives thereof with glyceryl monooleate or glyceryl monostearate (B2) and at least one at least trifunctional alcohol (Cx) selected from glycerol, diglycerol, triglycerol, trimethylolethane, trimethylolpropane, 1,2,4-butanetriol, pentaerythritol, tris(hydroxyethyl) isocyanurate and polyetherols thereof based on ethylene oxide and/or propylene oxide as demulsifiers for splitting crude oil emulsions. The demulsifiers described there are still in need of improvement with regard to their splitting action.